The invention relates to a motor vehicle having multi-axle drive and controls thereof.
Such drive concepts are known in various cross-country vehicles that use so-called free-wheel hubs as the wheel couplings and where the transfer transmission and the differential lock can be shifted electrically or electropneumatically or electrohydraulically by hand. The structural elements that are intended for the connectable drive are designed for high running outputs since, at least theoretically, there is the possibility that this drive is connected permanently.
It is the objective of the invention to improve the known drive of the above-mentioned type in such a way that the driver is relieved from the decision concerning the connecting or disconnecting of locks and couplings and that nevertheless no or no significant additional costs will occur.
According to the invention, this objective is achieved by a system that automatically shifts the differential and transfer transmission lock and wheel couplings. By means of the automatic shifting of the lock and of the couplings, it is ensured that the drive that can be connected is connected only when it is really required. It may therefore be designed for lower running outputs and, as a result, is less costly to manufacture. This absorbs, at least partially, the additional costs that can be reduced further by the predominant operation in the single axle drive and the resulting savings of fuel costs.
The system includes a first comparator or an a slip control system for receiving the output signal of the speed sensors for the permanently driven wheels and emitting an output control signal when the speed exceeds a given value to control the to lock the differential or to provide braking respectfully. A second comparator forms a median speed signal from the output sensors of all the wheels, determines a threshold value from the median speed, compares the individual wheel speeds with the assigned threshhold value and emits an output when the speed sensor outputs exceed the assigned threshhold value. A third comparator forms a quantity characteristic of the driving condition of the motor vehicle from the speed sensors for the connectable driven wheels and a steering angle sensor and emits an output when this quanity exceeds a fixed value assigned to the steering angle or the driving speed. A fourth comparator provides a first output signal when the output signal of the speed comparator of the output shaft from the transfer transmission to the connectable wheels is within the tolerance range of the output signal of the speed sensor of the most slowly turning connectible wheel and a second output when the output of the third comparator and the first output of the fourth comparator exists simultaneously. A first OR-gate has an imput from the second comparator and the second output of the fourth comparator for providing a control signal to the coupling of the transfer transmission. A second OR-gate receives an input from the third comparator and the first output of the fourth comparator and provides an output signal to control the wheel couplings of the connectable driven wheels. A monostable circuit may be provided to the output of the third comparator to prolong the output signal for an indicated period of time. The first output of the fourth comparative may be replaced by the output signal from the second comparator that is delayed by a time delay circuit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.